Abstract
Many terrestrial and aquatic taxa are known to form periodic aggregations, whether across life history or solely during specific life stages, that are generally governed by the availability and distribution of resources. Associations between individuals during such aggregation events are considered random and not driven by social attraction or underlying community structure. White sharks (Carcharodon carcharias) have been described as a species that exhibits resource-driven aggregative behaviors across ontogenetic stages and juvenile white sharks are known to form aggregations at specific nursery sites where individuals may remain for extended periods of time in the presence of other individuals. We hypothesized juvenile white sharks form distinct communities during these critical early phases of ontogeny and discuss how a tendency to co-occur across life stages may be seeded by the formation of these communities in early ontogeny. We present results from a series of social network analyses of 86 juvenile white sharks derived from 6 years of passive acoustic telemetry data in southern California, demonstrating the likelihood of association of tagged juvenile white sharks is greater when sharks are of similar size-classes. Individuals in observed networks exhibited behaviors that best approximated fission-fusion dynamics with spatiotemporally unstable group membership. These results provide evidence of possible non-resource driven co-occurrence and community structure in juvenile white sharks during early life stages.
Highlights
Sociality, or the propensity of individuals to form social groups (Merriam-Webster., 2021), is a trait exhibited across taxa and varies between loose temporary aggregations to life-long associations (Alexander, 1974; Sabol et al, 2020)
Animal social groups are characterized by motivated cohesion and can be distinguished from aggregative behaviors, which are temporary assemblages of individuals in response to non-social forcing factors, such as seasonal resource availability (Jacoby et al, 2011; Meese and Lowe, 2019; Grueter et al, 2020)
A previous study demonstrated post-release survival rates of juvenile white sharks retrieved live from gillnets to be in the order of 93% (Lyons et al, 2013), while a more recent analysis indicated that minimizing handling and on-deck holding times may in turn minimize non-lethal post-release negative effects (Raoult et al, 2019)
Summary
The propensity of individuals to form social groups (Merriam-Webster., 2021), is a trait exhibited across taxa and varies between loose temporary aggregations to life-long associations (Alexander, 1974; Sabol et al, 2020). Findlay et al (2016) reported that associations between white sharks in their study were random, they exhibited weak structuring by sex and body size, whereas Schilds et al (2019) reported nonrandom, sex-dependent associations with temporal variability. These studies drew upon observations of sub-adult and adult sharks co-occurring under baited and chummed (burleyed) conditions, at locations proximal to pinniped haul-outs, with very different time thresholds constituting co-occurrence. Preliminary high-spatial-resolution movement data derived from hyperbolic positioning via a high density acoustic array off Carpinteria, California, indicate individual juvenile white sharks form aggregations (5–30 individuals of multiple size-classes) and use overlapping, spatially restricted areas (∼8 km2) continuously, for periods of weeks to months (Spurgeon et al, unpublished data; Anderson et al, 2021b)
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